1. Related Technical Fields
Related technical fields include traffic-jam state calculation systems that calculate a traffic-jam state of a link.
2. Related Art
Conventional portable information apparatuses or personal computers are capable of displaying maps of desired areas to users by using map information is stored in memory devices downloaded from servers. The portable information apparatuses include, for example, vehicle-mounted navigation systems, personal digital assistants (PDAs), portable telephones, and the like. The map information includes, for example, names of ordinary roads and highways, and facility names. Such systems not only display maps but may also provide traffic information, such as information concerning traffic jams or the like, in order to improve the convenience. One system that provides such traffic information is the vehicle information communication system (VICS®).
VICS is a system in which sensors provided on roads detect vehicles traveling on the roads, and a VICS center collects the detected data, generates traffic information (VICS information), and provides the VICS information to terminals such as car navigation systems or the like. However, the VICS information can be obtained only from major roads on which the sensors are provided. Thus, there is a problem in that the VICS only covers a limited area.
Thus, a probe-car system has been studied as a new system for obtaining traffic information. In the probe-car system, a traveling vehicle (probe car) is used as a sensor (probe), information measured in the traveling vehicle (probe information) is collected, and traffic information is generated.
Here, the probe-car system has an advantage in that real-time data can be collected from a much wider area compared with the VICS.
In Japanese Unexamined Patent Application Publication No. 2005-209153 (pp. 5-6, Table 2, and FIG. 2), the degree of a traffic jam generated from probe information is included in traffic information provided to users and is used for identifying how severe the traffic jam is. For example, there are three classifications of a traffic jam: a “serious traffic jam,” a “moderate traffic jam,” and “no traffic jam” listed from the highest degree to the lowest degree.
A link is classified into one of the classifications on the basis of an average speed of vehicles traveling on the link and predetermined thresholds (for example, on an ordinary road, the threshold between a “serious traffic jam” and a “moderate traffic jam” is 12 km/h, and the threshold between a “moderate traffic” and “no traffic jam” is 32 km/h). The degree of a traffic jam into which the link has been classified is provided to the users as traffic information.